The present invention relates to a manufacturing method for a plasma display panel used to display images on computer monitors, televisions and the like.
The following is an explanation of a display panel in the related art with reference to the drawings. FIG. 21 is a simplified cross sectional of an alternating current (AC) plasma display panel (hereafter referred to as a PDP).
In FIG. 21, discharge electrodes 211 are formed on a front glass plate 210. These are then covered by a layer of dielectric glass 212 and a protective dielectric layer 213, composed of magnesium oxide (MgO). A description of this technique may be found in Japanese Laid-Open Patent No. 5-342991.
Address electrodes 221 are formed on a rear glass plate 220, and covered by a visible light reflective layer 222 and partitions 223. A phosphor layer 224 is placed on top of this. Spaces 230 are discharge spaces which enclose a discharge gas. Three types of phosphors, for producing the colors red, green and blue, are arranged in order in the phosphor layer 224 to produce a color display. The phosphors in layer 224 are excited by short-wave ultra-violet rays generated by electric discharge on a wavelength of 147 nm for example, and emit visible light.
The phosphors that make up the phosphor layer 224 are generally produced using these compounds:
Blue phosphor: BaMgAl10O17:Eu
Green phosphor: Zn2SiO4:Mn or BaAl12O19:Mn
Red phosphor: Y2O3:Eu or (YXGd1xe2x88x92x) BO3:Eu
The following is an explanation of a PDP manufacturing method in the related art.
Firstly, discharge electrodes are formed on a front glass plate, and a dielectric layer made from dielectric glass is formed to cover the discharge electrodes. A protective layer made from MgO is formed on top of the dielectric layer. Next, address electrodes are formed on a back glass plate, and a visible light reflective layer made from dielectric glass formed on top of this. Then glass partitions are produced on top of this at fixed intervals.
A phosphor layer is formed by alternately introducing phosphor pastes for the red, green and blue phosphors produced as above into the spaces between the partitions. Next this phosphor layer is baked at a temperature of around 500xc2x0 C. to eliminate resin and similar substances from the paste (Phosphor Baking Process).
After the phosphor layer has been baked, a glass frit for sealing the front and back plates together is applied to the edge of the back glass plate, and then pre-baking is performed at around 350xc2x0 C. to eliminate resin and the like from the glass frit (Sealing Process, Pre-baking Process).
After this, the front glass plate, formed from the discharge electrodes, the dielectric glass layer and the protective layer, and the back glass plate are placed together with the partitions sandwiched between them and the display electrodes and address electrodes at right angles. The panel is then heated at around 450xc2x0 C. to seal the edges of the plates together with glass frit (Sealing Process).
After this, the inside of the panel is evacuated by heating it to a certain temperature of around 350xc2x0 C. (Evacuation Process) and a discharge gas is introduced at a certain pressure once this process is completed.
A panel manufactured using the above processes exhibits great variations in luminescence and discharge characteristics during the initial stage of ignition. Accordingly, luminescence and discharge characteristics need to be stabilized by ensuring that the manufactured panel discharges electricity only during a certain time period. This process is known as the aging process.
However, in the PDP manufacturing process used in the related art, a particular problem is posed by the fact that the aging process for stabilizing the luminescence and discharge characteristics actually causes a deterioration in the luminescence characteristics.
One reason for this is the deterioration in the phosphors used. The compound BaMgAl10O17:Eu used as a blue phosphor is particularly prone to deterioration during the aging process, resulting in a decrease in luminous intensity and a deterioration in luminescent chromaticity.
In view of the above problems, the object of the present invention is to provide a PDP that may undergo the necessary aging process with minimal phosphor deterioration, and that has a comparatively high luminous efficiency as well as high-quality color reproduction.
In order to achieve the above object, a PDP manufacturing process is performed in the following way. First, a front plate and a back plate, on at least one of which discharge electrodes have been arranged and on at least one of whose inner surfaces a phosphor layer has been formed are sealed together so that an inner space is formed between them. Then an aging process in which a required discharge voltage is applied to the discharge electrodes is performed. The aging process includes an introducing process in which a discharge gas with a partial steam pressure of 15 Torr or less is newly introduced into the inner space from the outside and an evacuating process, in which discharge gas is evacuated from the inner space. By performing the introducing process together with the evacuating process, discharge gas can be circulated continuously or intermittently through the inner space, while a required discharge voltage is applied to the discharge electrodes, thereby enabling discharge to be produced.
Furthermore, a PDP manufacturing process may be performed in the following way. First, a front plate and a back plate, on at least one of which discharge electrodes nave been arranged and on at least one of whose inner surfaces a phosphor layer has been formed are sealed together so that an inner space is formed between them. Then an aging process in which a required discharge voltage is applied to the discharge electrodes is performed. The aging process includes an introducing process in which a discharge gas with a partial steam pressure of 15 Torr or less is newly introduced into the inner space from the outside and an evacuating process, in which discharge gas is evacuated from the inner space. The discharge generated when a required discharge voltage is applied to the discharge electrodes is divided into a plurality of discharge periods. By performing the introducing and evacuating processes in the intervals between discharge periods, discharge gas can be circulated through the inner space.
Here, the introducing process introduces gas via a first air vent formed in the panel, and the evacuating process evacuates gas via a second air vent formed in the panel.
Consequently, the PDP subject to the aging process has the following structure. A plurality of discharge spaces are formed by arranging a plurality of partitions to divide up the inner space between the front plate and the back plate, and a sealing glass layer for sealing the panel is included between the perimeters of the front plate and the back plate. Then a first space connected to the discharge spaces formed by the plurality of partitions is formed between first ends of the plurality of partitions and the sealing glass layer, and a second space connected to the discharge spaces is formed between second ends of the plurality of partitions and the sealing glass layer.
The first air vent forms a connection with the first space and the second air vent with the second space. Then this structure is subject to an aging process in which the discharge gas is circulated through the discharge space. This is achieved by performing the introducing process by introducing the discharge gas into the first space via the first air vent, and the evacuating process by evacuating the discharge gas from the second space via the second air vent.
The PDP subjected to the aging process further includes a structure in which a minimum distance between partition ends of the plurality of partitions, excluding at least a partition furthest from the first air vent, and the sealing glass layer bordering the first space is more than a minimum distance between the sealing glass layer parallel to the partitions and an adjacent partition.
The PDP subjected to the aging process further includes a structure in which one part of each of the outermost partitions among the plurality of partitions is connected with one part of the sealing glass layer to prevent discharge gas from flowing into space between the outermost partitions and the sealing glass layer.
The PDP subjected to the aging process further includes a structure in which the first air vent is formed in the vicinity of one of the outermost partitions, and the second air vent is formed in the vicinity of the other outermost partition, on the opposite side to the first air vent.
A plurality of discharge spaces are formed by arranging a plurality of partitions to divide up the inner space between the front plate and the back plate and a sealing glass layer for sealing the panel is included between the perimeters of the front plate and the back plate. A barrier is further included between the front and back plates around the inside of the sealing glass layer. Then a first space connected to the discharge spaces formed by the plurality of partitions is formed between first ends of the plurality of partitions and the barrier, and a second space connected to the discharge spaces is formed between second ends of the plurality of partitions and the barrier. The first air vent forms a connection with the first space and the second air vent with the second space. Here the above structure is subject to an aging process in which the discharge gas is circulated through the discharge space. This is achieved by performing the introducing process by introducing the discharge gas into the first space via the first air vent, and the evacuating process by evacuating the discharge gas from the second space via the second air vent.
The PDP subject to the aging process further includes a structure in which a minimum distance between partition ends of the plurality of partitions, excluding at least a partition furthest from the first air vent, and the barrier bordering the first space is more than a minimum distance between the barrier parallel to the partitions and an adjacent partition.
The PDP subject to the aging process further includes a structure in which one part of each of the outermost partitions among the plurality of partitions and one part of the barrier are connected to prevent discharge gas from flowing into space between the outermost partitions and the barrier.
The PDP subject to the aging process further includes a structure in which the first air vent is formed in the vicinity of one of the outermost partitions, and the second air vent is formed in the vicinity of the other outermost partition, on the opposite side to the first air vent.
In this kind of structure discharge gas mainly flows through a plurality of gas passages leading from the first space to the second space. This prevents deterioration in the phosphors during the aging process.
The partial pressure of steam contained in the discharge gas introduced into the inner space should preferably be 10 Torr or less, 5 Torr or less, 1 Torr or less or even 0.1 Torr or less.
An inert gas may be used as the discharge gas introduced into the inner space. Helium, neon, argon or xenon may be used as this gas.
In order to achieve the above object, a PDP manufacturing process is further performed in the following way. First, a front plate and a back plate, on at least one of which discharge electrodes have been arranged and on at least one of whose inner surfaces a phosphor layer has been formed are sealed together so that an inner space is formed between them. Then a heating process for heating phosphors in the phosphor layer is performed after the aging process has been completed. This heating process enables the characteristics of the phosphors to be restored.
The heating process following the aging process should preferably heat the phosphors to as high a temperature as possible, specifically of 300xc2x0 C. or more. If possible, the phosphors should be heated to an even higher temperature, such as 370xc2x0 C. or more, 400xc2x0 C. or more or even 500xc2x0 C. or more.
The phosphors may be heated by heating the whole panel in an oven at a specified temperature, by concentrating a laser beam on the part of the panel on which the phosphors are arranged or by circulating a heating medium through the inner space. If the whole panel is heated using an oven, the panel cannot be heated at a temperature higher than the softening point of the glass used to seal the front and back plates of the panel together. If the more localized methods of a laser beam or heating medium are used to heat the panel, however, it can be heated to a higher temperature.
The heating process following the aging process (if heating in an oven or using a laser) should preferably be performed while the gas in the inner space is being evacuated. The heating process following the aging process (if heating in an oven or using a laser) may also be performed by heating the panel after the gas in the inner space has been evacuated and dry gas introduced.
The heating process following the aging process (if heating in an oven or using a laser) may also be performed by heating the panel while dry gas is circulated through two or more air vents formed in the panel.
The dry gas may be an inert gas, and preferably should include oxygen.
The introduced dry gas may also be evacuated from an inner space heated by the heating process following the aging process (if heating in an oven or using a laser) while the panel is still hot.
If the heating process takes place with gas still circulating through the discharge space (if heating in an oven while gas is circulating in the discharge space, or using a laser or a heating medium), the rate of exchange is higher if the structure subjected to the heating process is one in which gas is circulated actively through the discharge space as described above, making this kind of structure preferable.
By using the above manufacturing method to restrict deterioration caused in particular to the blue phosphor, a PDP with superior luminescence characteristics can be obtained. Specifically, a PDP in which a color temperature of light emitted when all of the cells are ignited by applying the same power to each cell is 7000 K can be obtained.
Furthermore, a PDP in which the peak intensity ratio for the light spectrums of blue light emitted by the blue cells and green light emitted by the green cells is greater than or equal to 0.8 can be obtained when cells in which blue and green phosphors have been arranged are ignited by applying the same power to each cell.